Presentation on theme: "Kinematic Analysis for A Conventional I.C. Engine P M V Subbarao Professor Mechanical Engineering Department Creation of Instantaneous Volume, Surface."— Presentation transcript:
Effect on Frictional Losses Engine friction is affected by the stroke-to-bore ratio because of two competing effects: Crankshaft bearing friction and power-cylinder friction. As the bore-to-stroke ratio increases, the bearing friction increases because the larger piston area transfers larger forces to the crankshaft bearings. However, the corresponding shorter stroke results in decreased power-cylinder friction originating at the ring/cylinder interface.
Instantaneous Heat Transfer (loss) form Cylinder
Gas to Surface Heat Transfer Heat transfer to walls is cyclic. Gas temperature T g in the combustion chamber varies greatly over and engine cycle. Coolant temperature is fairly constant. Heat transfer from gas to walls occurs due to convection & radiation. Convection Heat transfer: Radiation heat transfer between cylinder gas and combustion chamber walls is
Instantaneous Heat Transfer (loss) from Cylinder Instantaneous surface area for heat transfer: Piston Speed
Effect on Heat Transfer Simple geometric relationships show that an engine cylinder with shorter bore -to- stroke ratio will have a smaller surface area exposed to the combustion chamber gasses compared to a cylinder with longer bore-to- stroke ratio. The smaller area leads directly to reduced in-cylinder heat transfer, increased energy transfer to the crankshaft and, therefore, higher efficiency.
Optimum Cylinder Geometry Identification of the optimum engine geometry that provides the best opportunity to have a highly efficient internal combustion engine is the first step in designing an engine. In-cylinder simulations have shown that the heat transfer increases rapidly above a bore-to-stroke ratio of about 0.5. Engine systems simulations have shown that the pumping work increases rapidly above a bore=to-stroke ratio of about 0.45. Engine friction models have shown that the crankshaft bearing and power-cylinder friction values, for the most part, cancel each other out for our opposed-piston, two- stroke engine.